1. Field of the Invention
This invention relates to improvements in an airbag of an airbag restraint system for protecting a vehicle passenger in the event of a serious vehicle collision or the like, and more particularly to a cloth constituting such an airbag as being connected to a gas generator and adapted to inflate upon being supplied with gas from the gas generator.
2. Description of the Prior Art
Hitherto a variety of airbag restraint systems have been proposed and put into practical use in the field of automotive vehicles. An example of the airbag restraint system is disclosed in Japanese Patent Publication No. 56-43890. An example of a device for securely retaining the airbag to a stationary side of the vehicle is disclosed in Japanese Utility Model Provisional Publication No. 54-69543.
Generally, such an airbag restraint system includes a gas generator which is fixed to a base plate installed to a stationary side of the vehicle such as an instrument panel or a steering wheel. An airbag is fixed to the base plate through a retainer and adapted to momentarily inflate upon being supplied with high pressure gas from the gas generator when the gas generator is operated in the event of a serious vehicle collision or the like.
The airbag is formed of cloth materials each of which is constituted of warp and weft yarns as basic materials. The warp and weft yarns are formed of high melting point polymer materials which have high melting points. The cloth materials are obtained by cutting a cloth in a manner to have predetermined shapes and areas.
For example, the airbag is formed of generally circular front and rear side cloth materials which are sewn at their peripheral portions with each other. The rear side cloth material is formed with a gas inlet opening through which high pressure gas from the gas generator is supplied.
Difficulties have been encountered in the above-described airbags of airbag restraint systems, in which fray is unavoidably made at the peripheral portions and the through-opening sections of the cloth materials in case of cutting the cloth materials by a press, thereby resulting in substandard airbags and degrading the efficiency of sewing operation of the airbag. In order to overcome these difficulties, it has been proposed to cut the cloth materials by using laser, a ultrasonic or cutter, a high frequency cutter. Additionally, the sewing operation is made upon folding the peripheral portions of the cloth materials.
However, the cutting by using laser or the like requires a high equipment cost and cannot improve the productivity of the airbag. Additionally such cutting techniques cannot be sufficiently effective to prevent the cloth materials from being frayed. The above-mentioned techniques of folding the peripheral portion of the cloth material peripheral portion is inferior from the economical view point particularly when a folded portion is large in size. Such folding also provides a disadvantage in that no folded portion can be formed particularly at the through-opening portions of the cloth material.
Furthermore, it has been also proposed to coat the cloth materials with a heat resistant synthetic resin material in order to prevent fray of the cloth materials. However, such a process for coating the resin material deteriorates the production line operation and makes the re-use of cloth materials difficult.